Identifying Metals and Their Physical Properties

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Identifying Metals andTheir Physical Properties

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Interest Approach

• Here are some different types of metals and
  alloys.
• Can you identify these metals?
• Do you see these broken parts made of different
  metals?
• How would you repair the broken parts?

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Student Learning Objectives

• Identify and explain the terms associated with
  metals.
• Describe the properties and structures of metals.
• Explain how steel is manufactured.
• Describe how metal is classified.
• Describe the characteristics used to identify
  metals.

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Terms

• Adhesion
• Alloy
• Annealing
• Casting
• Compressive strength

• Crystal structure
• Fatigue strength
• Flexure strength
• Hardening
• Hardness

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Terms

• High temperature creep
• Impact strength
• Malleable
• Shear strength

• Space lattice
• Steel
• Tempering
• Tensile strength

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What terms are commonly used with metals?
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Because of the widespread use and necessity for
metals in agriculture, it is important for the
worker to have a basic understanding of metals
and metallurgy when fabricating and making
repairs on metals.
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Metal

• Metal is an element.
• There are over 100 known elements, and about 75
  percent of them are classified as metals.

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Alloy

• An alloy is a mixture of two or more metals, or
  of metals and one or more non-metals
• The elements added to a metal to form an alloy
  may be either metal or non-metal.
• In most cases alloys have more desirable
  properties and are less expensive than pure
  metals.

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High Temperature Creep

• High temperature creep is the slow stretching of
  steel under stress at high temperatures.

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Adhesion

• Adhesion is the sticking together of two unlike
  metals involving a mechanical bond.
• The mechanical bond involves the flowing of a
  metal in a liquid form into the pores of a metal
  in a solid form.

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Annealing

• Annealing is the softening of metal and removing
  of the brittleness.
• The annealing process is done by heating the
  metal to a cherry red and then allowing it to
  cool slowly in vermiculite, dry hot sand, or a
  furnace.

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Tempering

• Tempering is obtaining the desired hardness and
  toughness in metal.

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The process of making steel harder is known as
hardening.

• This is done by heating the steel to a cherry red
  color, then cooling it quickly in water.
• Hardened steel is not only extremely hard but
  also brittle.
• Hardening is the first step in tempering.
• Hardness is the ability of a material to resist
  being indented.

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Casting

• Casting is pouring melted metal into a mold so
  that it will be a certain shape after cooling.

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Malleable

• The capability of being extended or shaped by
  being beaten with a hammer or by being pressed by
  rollers is known as malleable.

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What are the properties and structures of metals?
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The distinct characteristics used to help
identify a given metal are referred to as its
properties.
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These characteristics include

• brittleness
• color
• corrosion resistance
• ductility
• malleability
• strength.

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These properties can be categorized into seven
broad classifications.
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1. Mechanical properties

• hardness
• brittleness
• ductility
• percent elongation
• toughness
• wear
• strength

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Tensile strength is the ability of a metal to
resist being pulled apart.
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Compressive strength is the ability of a metal to
resist deformation by forces pushing it together.
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Shear strength is the ability of a metal to
resist forces acting in opposite directions.
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Fatigue strength is the ability of a metal to
take repeated loads without deforming.
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• Impact strength is the ability of a metal to
  resist shock.
• Flexure strength is the ability of a metal to
  bend without deforming or breaking.

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2. Chemical properties

• refers to the chemical make-up of the metal and
  its ability to resist reaction with the
  environment.

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2. Chemical properties

• Chemical properties are oxide or compound
  composition, acidity or alkalinity of the metal
  corrosion resistance resistance to acids and
  salts and resistance to other chemicals.
• Corrosion resistant metal will resist
  deterioration from heat, sunlight, water, and
  humidity.

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3. Physical properties

• relates to the dimensions, shape, specific
  gravity, and weight of the metal.

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4. Thermal properties

• Characteristics such as
• expansion
• contraction
• thermal conductivity
• specific heat

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5. Optical properties

• luster
• color
• light transmission
• light reflection

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6. Electromagnetic properties

• electrical conductivity
• magnetic permeability
• galvanic action

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7. Acoustical properties

• relate to the ability of a metal to transmit and
  reflect sound

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Crystal Structure

• The crystal structure of a metal is the way
  molecules of a substance are arranged or how they
  are packed or fitted together.
• The pattern these atoms make is called a space
  lattice.

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Crystal Structure

• There are 14 lattices involved in the study of
  metals
• Only three of the most common structures are of
  real importance here.

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Crystal Structure

• The body-centered cubic arrangement has nine
  atoms.
• The main characteristic is their strength and the
  difficulty with which they are worked when cold.
• Examples iron, molybdenum, chromium, tungsten,
  and vanadium at room temperature.

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Crystal Structure

• The face-centered cube arrangement has fourteen
  atoms.
• The main characteristic is that they are plastic
  and malleable.
• Examples iron, aluminum, nickel, copper, lead,
  platinum, and silver.

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Crystal Structure

• The close-packed hexagon arrangement has
  seventeen atoms.
• The main characteristics are that they are
  non-plastic and must be heated before they can be
  worked.
• Examples cadmium, cobalt, bismuth, magnesium,
  titanium, and zinc.

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How is steel manufactured?
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Steel is an alloy of iron and carbon and usually
other metals.
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There are hundreds of different steels, ranging
in composition from 99 percent iron and very
small amounts of carbon, to steels containing
less than 55 percent iron and a large percentage
of other metals.
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There are four major steel making processes

• the Bessemer furnace
• the open hearth furnace
• electric furnace
• the oxygen furnace

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There are four major steel making processes

• All four processes are similar in principle in
  that pig iron is treated with an oxygen-bearing
  material to burn out the carbon and impurities.
• Alloying metals are then added.

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There are two general types of steel carbon and
alloy.

• Approximately 80 to 90 percent of steel produced
  is carbon steel.
• Carbon steels contain 0.05 to 1 percent carbon
  and less than 1.5 percent of the other elements.

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There are two general types of steel

• The strength of steel increases as the carbon
  content increases, but the hardness, brittleness,
  and difficulty of fabrication also increase.
• There are hundreds of alloy steels.
• The effects of additives varies.
• Some of these effects are as follows

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Additive Effects

• Chromium makes the alloy hard and increases the
  wear and corrosion resistance of steel.
• Steels containing more than 4 percent chromium
  are called stainless steels.
• Sulfur is added to aid in machinability of the
  steel.

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Additive Effects

• Silicon is added to improve the electrical,
  mechanical, and thermal characteristics.
• Nickel is added to increase the toughness and
  strength.
• Vanadium is added to increase the strength.

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Additive Effects

• Tungsten is used to produce tool steels that will
  maintain a cutting edge at high heat.
• Aluminum helps to provide a hardened surface.
• Molybdenum tends to increase the hardness and the
  endurance limits of steel.

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Additive Effects

• Oxygen forms iron oxide which is not desirable.
• Phosphorus is found in all steels.
• When present in high percentages it is considered
  an impurity.
• At low percentages it improves machinability.

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Additive Effects

• Carbon added to iron changes the physical
  properties.
• The amount of change is directly proportional to
  the amount of carbon added to the iron.

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How is metal classified?

• Of the known elements, about 80 to 90 are
  technically considered metals.
• Of these, 10 to 15 are considered important in
  agricultural mechanics.
• These metals can be broken down into four groups
  and classified as follows

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How is metal classified?

• These metals can be broken down into four groups
  and classified as follows
• Ferrous Metals
• Non-ferrous metals
• Ferrous Alloys
• Non-ferrous Alloys

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A. Ferrous metals

• Metals whose chief ingredient is iron.
• Pig iron, cast iron, wrought iron, and steel are
  examples.

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Pig iron or cured iron

• is iron ore changed to pig iron by a blast
  furnace.

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Cast iron

• is a product of pig iron and contains a
  considerable amount of carbon and some
  impurities.
• It is brittle and granular in structure. It is
  formed by pouring into special castings.

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Cast iron

• Gray cast iron has been cooled slowly, allowing
  carbon to separate from the iron into pockets of
  carbon in the form of graphite.
• Gray cast iron is used in sprockets, stoves, and
  manifolds.

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Cast iron

• White cast iron has been cooled quickly to
  prevent separation of carbon.
• White cast iron is used for agitators in grain
  drills.

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Cast iron

• Malleable cast iron has been made soft, strong,
  and malleable through a long re-heating and
  cooling process called annealing.
• Malleable cast iron will bend slightly, such as
  for a conventional mower guard.

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Wrought iron

• a product of pig iron that has had most of the
  carbon removed, is a two-component metal
  consisting of high purity iron and iron silicate.
  
• Wrought iron is the only ferrous metal that
  contains siliceous slag.

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Wrought iron

• The slag is responsible for the desirable
  properties of wrought iron, particularly its
  resistance to corrosion and fatigue.
• It is used for rivets, porch furniture, and
  decorative roof supports.

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Steel

• is iron characterized chiefly by its carbon
  content.

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B. Non-ferrous metals

• are those which have no iron and are made up of a
  single element.
• These are aluminum, copper, lead, magnesium,
  nickel, tin, tungsten, zinc, silver, and gold.

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Aluminum

• is a silver-white, malleable, ductile metal.
• It is known for its electrical conductivity,
  heat conductivity, rust resistance, and light
  weight.

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Copper

• reddish-brown in color
• is used for tubes, wire, sheets, and plates.
• It has excellent workability, either hot or cold,
  and the highest electrical and heat conductivity
  of all commercial metals.

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Lead

• has a bluish-white color and a bright luster.
• It is soft, highly malleable, and ductile has
  slight tenacity and is a poor conductor of
  electricity.
• It is used for making pipe and containers for
  corrosive liquids.

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Magnesium

• is a very lightweight, silver-white metal, which
  is malleable and ductile and burns in air.
• It is usually found in the alloy known as
  dowmetal.
• It is useful for airplane bodies, truck and auto
  wheels, ladders, lawn mower frames, and any place
  where weight reduction is important.

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Nickel

• is a hard, malleable, ductile, tenacious white
  metal that is somewhat magnetic.
• It is valuable for the alloys it forms with
  other metals.

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Tin

• does not corrode in humid conditions, adheres
  tenaciously to iron, has a low melting point
• used extensively in solder, brass, bronze, and
  pewter.

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Tungsten

• one of the heaviest metals
• used for making filaments for incandescent lamps.
  
• Tungsten carbide is almost as hard as diamond and
  is used extensively for cutting tools.

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Zinc

• bluish-white metal at ordinary temperatures
• is brittle but malleable at high temperatures
• used as a galvanizing metal coating to prevent
  corrosion.

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Silver

• shiny, white metal
• used mostly for ornamental work, jewelry, and
  table-ware.
• Silver is the best conductor of electricity.

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Gold

• is most often used for ornamental jewelry.

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C. Ferrous alloys

• Metals made up largely of ferrous materials but
  having other elements in sufficient quantities to
  change the ferrous characteristics.

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Manganese steel

• can stand strain, hammering, shock, and hard
  wear.
• It is used for the jaws of ore crushers, power
  shovels, chains, gears, and safes.

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Chromium steel

• resists rust, shock, scratches, and stains.
• It is used for bearings, safes, ore crushers, and
  is the basis for high-quality stainless steel.

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Nickel steel

• is strong, hard, elastic, tough, and durable.
• It does not rust easily
• used for springs, cables, axles, shafts, and
  armor plate.

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Stainless steel

• seldom rusts
• used for cutlery, precision measuring
  instruments, dentistry supplies, auto parts, and
  engine valves.

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Tungsten steel

• adds hardness to steel and allows it to withstand
  heat.
• Tungsten carbide is the hardest metal known and
  is used for various cutting surfaces.

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Molybdenum steels

• known for their strength and hardness
• used for hacksaw blades, high-grade machinery
  parts, bearings, and auto parts.

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Vanadium steel

• is tough and can withstand great shocks as well
  as resist corrosion.
• used for springs, gears, and vibrating parts of
  machinery.

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High-speed steel

• contains one or more alloying elements

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D. Non-ferrous alloys are made up of two or more
nonferrous elements.
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Brass

• an alloy of copper and zinc.
• It is ductile, malleable, and acid resistant.

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Bronze

• an alloy of copper and tin
• behaves very much like brass when welded.

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Solder types

• lead and tin solder
• copper and zinc alloy solder
• silver and copper alloy solder.

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Pewter

• an alloy of 92 percent tin, 5 percent antimony
  and 3 percent copper.

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Monel

• is an alloy of 60 percent nickel and 40 percent
  copper.

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Grading and classifying steel.

• Because steel varies in carbon content and
  alloying elements, a system to group it using
  standards established by the Society of
  Automotive Engineers (SAE) was developed.

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Grading and classifying steel

• In the SAE numbering system, the first digit
  indicates the general type of steel.
• The second digit indicates the percentage of the
  main alloy in the steel.

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Grading and classifying steel.

• The third and fourth digits show the percent of
  carbon in the steel in hundredths of one percent.

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What characteristics are used to identify metals?

• Physical and chemical tests are used to determine
  the type of metal.
• Because so many kinds of metals are used in
  agriculture it is very important that you learn
  to identify them.

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The Appearance Test

• involves identification of a metal by its
  appearance and use.
• Color and appearance make certain metals such as
  copper, brass, and bronze easy to identify.

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The Magnetic Test

• involves identification of metal by the use of a
  magnet.

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The Chisel Test

• involves identification of metal by the use of a
  hammer and cold chisel.

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The Fracture Test

• involves identification of metal by fracturing
  the metal and observing the grain.

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The Flame Test

• involves identification of metals by applying a
  flame to them and watching what occurs.

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The Spark Test

• involves identification of metals by applying
  them to a grinding wheel and observing the spark
  that is generated.
• The color, shape, average length, and activity
  of the sparks are characteristics of the material
  being tested.

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Student Activity

• Identify the various metals given using the
  following materials

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Handouts of Metal Identification
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Lab Sheet
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Various testing items

• Grinder
• Magnet
• Hammer and Chisel
• Oxyacetylene flame
• Vise

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Review

• Identify and explain the terms associated with
  metals.
• Describe the properties and structures of metals.
• Explain how steel is manufactured.
• Describe how metal is classified.
• Describe the characteristics used to identify
  metals.